Method and apparatus for efficient link redundancy

ABSTRACT

A method that changes the selection of a 2:1 multiplexer that receives a first output signal from a first framer and a second output signal from a second framer. The first output signal is the same as the second output signal. An apparatus having a framer and a 2:1 multiplexer that receives an inbound signal from the framer. A first mutliplexer receives at least one signal from another framer and the 2:1 multiplexer has an input coupled to an output from the first multiplexer. A second multiplexer receives at least one signal from the other framer and the second multiplexer has an output coupled to an input of the framer for an outbound signal.

FIELD OF THE INVENTION

The field of invention relates to networking, generally, and, more specifically, to link redundancy.

BACKGROUND

Framers are commonly used in networking systems. FIG. 1 illustrates an exemplary framer. A network line such as networking line 102 or networking line 103 in FIG. 1 couples a pair of networking systems (e.g., switches, routers, multiplexers, gateways, etc.) so that the pair of networking systems may communicate with one another. Examples of networking lines include fiber optic or copper cable. Note that for simplicity, physical layer devices (e.g., lasers/photo-detectors, line drivers, etc.) typically placed between the framer 101 and the networking lines are not shown in FIG. 1.

Frames (such as frames 108, 109, and 110) are used to organize the flow of information over a network line. In the case of SYNnchronous Optical Network (SONET) frames, each frame may be viewed as carrying “n” synchronous payloads envelopes (SPEs) of 810 bytes. Conceptually, as seen in FIG. 1, frame 108 carries SPEs 111 ₁, 111 ₂, 111 ₃, . . . , 111 _(n); frame 109 carries SPEs 112 ₁, 112 ₂, 112 ₃, . . . , 112 ₃; and frame 110 carries SPEs 113 ₁, 113 ₂, 113 ₃, . . . , 113 _(n). For simplicity, note that the overhead portions of each frame 108, 109, 110 are not shown.

For SONET frames, the time consumed by each frame (e.g., time T1 for frame 108, time T2 for frame 109, and time T3 for frame 110) corresponds to 125 μs regardless of the number of SPEs carried per frame (i.e., “n”). Furthermore, the number of SPEs carried per frame remains constant from frame to frame. Thus, the number of SPEs carried per frame is indicative of the network line speed.

For example, a SONET networking line having only one SPE per frame (i.e., n=1) corresponds to a line speed of 51.840 Mbs (i.e., 810 bytes every 125 μs). Similarly, a SONET networking line having three SPEs per frame (i.e., n=3) corresponds to a line speed of 155.52 Mbs (i.e., 2430 bytes every 125 μs), a SONET networking line having forty eight SPEs per frame (i.e., n=48) corresponds to a line speed of 2.488 Gb/s (i.e., 38880 bytes every 125 μs), etc. Note that if the applicable networking line is optical “OC” is typically used instead of “STS” (e.g., OC-3, OC-48, etc.).

One SPE per 125 μs is referred to as an STS-1 signal. Thus, a 51.840 Mbs SONET networking line carries a single STS-1 signal; a 155.52 Mbs SONET networking line carries three STS-1 signals; and a 2.488 Gb/s SONET networking line carries forty eight STS-1 signals. Typically, each STS-1 signal may be viewed as corresponding to the same SPE position across different frames. That is, a first STS-1 signal corresponds to SPEs 111 ₁, 112 ₁, and 113 ₁; a second STS-1 signal corresponds to SPEs 111 ₂, 112 ₂, 113 ₂; etc.,.

FIG. 1 shows a framer within a networking system 110 that acts as a node in a network. The framer 101 in FIG. 1 is one or more semiconductor chips that provide framing organization for a network line. For example, the exemplary framer 101 of FIG. 1: 1) formats STS-1 signals into frames that are transmitted on an outbound networking line 103 to another network node; and 2) retrieves STS-1 signals from frames received from another network node on an inbound networking line 102.

In the case of outbound transmission, other portions of the framer's networking system 110 individually provide each STS-1 signal carried by the outbound network line 103 to the framer 101. For example, a first STS-1 signal is presented to the framer at input 107 ₁, a second STS-1 signal is presented to the framer at input 107 ₂, etc. Consequently, for example, the framer 101 maps on outbound networking line 103: the STS-1 signal received at input 107 ₁ across SPE positions 111 ₁, 112 ₁, 113 ₁; the STS-1 signal received at input 107 ₂ across SPE positions 111 ₂, 112 ₂, 113 ₂, etc.

Correspondingly, in the case of inbound transmission, each STS-1 signal carried by the inbound network line 102 is individually presented by the framer 101 to higher layers of the framer's networking node 110. For example, a first STS-1 signal mapped on SPE positions 111 ₁, 112 ₁, 113 ₁, is presented on framer output 106 ₁, a second STS-1 signal mapped on SPE positions 111 ₂, 112 ₂, 113 ₂ is presented on framer output 106 ₂, etc. The individual outbound STS-1 signals may be collectively referred to as outbound STS-1 signals 105. Similarly, the individual inbound STS-1 signals may be collectively referred to as inbound STS-1 signals 104.

Note that different types of framers may exist. In one respect, the granularity of the inbound and outbound signals 104, 105 may vary. For example, with respect to SONET framers, each of the individual signals that collectively form the inbound and outbound signals 104, 105 may be comprised of a signal that consumes less bandwidth than an STS-1 signal (e.g., down to a 64 kbps signal) or more bandwidth than an STS-1 signal (e.g., each input signal may correspond to a group of STS-1 signals such as an STS-3 rate signal or an STS-12 rate signal, or higher). In another respect, different framing formats may be applied (e.g., SDH).

SUMMARY OF INVENTION

A method that changes the selection of a 2:1 multiplexer that receives a first output signal from a first framer and a second output signal from a second framer. The first output signal is the same as the second output signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not limitation, in the Figures of the accompanying drawings in which:

FIG. 1 shows an exemplary framer;

FIG. 2 shows an exemplary framer logic unit;

FIG. 3 shows a 1+1 FFP PG or UPSR redundancy scheme that employs the exemplary framer logic unit of FIG. 2;

FIG. 4 shows an example of 1:N redundancy or 1:1 BLSR redundancy implemented with the framer logic unit 200 shown in FIG. 2; and

FIG. 5 shows the exemplary framer logic unit of FIG. 2 further including a switching or routing extension.

DETAILED DESCRIPTION

A method is described that changes the selection of a 2:1 multiplexer that receives a first output signal from a first framer and a second output signal from a second framer. The first output signal is the same as the second output signal.

An apparatus is described having a framer and a 2:1 multiplexer that receives an inbound signal from the framer. A first mutliplexer receives at least one signal from another framer and the 2:1 multiplexer has an input coupled to an output from the first multiplexer. A second multiplexer receives at least one signal from the other framer and the second multiplexer has an output coupled to an input of the framer for an outbound signal.

Link redundancy is a technique for protecting against the failure of a network line. A networking line may fail for any of a number of reasons (e.g., the line itself may be opened, the aforementioned physical layer devices may fail, etc.). As such, networking service providers and networking system providers are interested in technology that allows for such failures without disrupting the operation of a network.

Link redundancy is the notion that a “spare” network line may be installed into the network for the purpose of carrying another network line's traffic should the other network line fail. That is, if a network line fails, the network “switches over” to the spare network line in order to avoid significant disruption of the network.

FIG. 2 shows an exemplary framer logic unit 200. The exemplary framer logic unit 200 of FIG. 2 provides for efficient link redundancy, as described in more detail with respect to FIGS. 3 and 4. Before discussing how the architecture of the framer logic unit 200 of FIG. 2 provides for efficient link redundancy implementation, however, the design of the framer logic unit 200 will first be discussed.

A framer 201 is shown coupled to an inbound networking line 202 and an outbound networking line 203. The framer 201 also provides inbound signals 204 from the inbound networking line 202 and receives outbound signals 205 for transmission over outbound networking line 203. In an embodiment, each signal corresponds to an STS-1 signal; however, other framer and signal embodiments may exist as alluded to in the background above.

Each inbound signal 206 ₁, 206 ₂, 206 ₃, . . . , 206 _(n) is directed from the framer 201 to its own corresponding 2:1 multiplexer 208 ₁, 208 ₂, 208 ₃, . . . , 208 _(n). That is, as seen in FIG. 2, inbound signal 206 ₁ is directed to 2:1 multiplexer 208 ₁; inbound signal 206 ₂ is directed to 2:1 multiplexer 208 ₂;, etc. The output of the framer logic unit 200 corresponds to the collective output 209 of each of the 2:1 multiplexers 208 ₁, 208 ₂, 208 ₃, . . . , 208 _(n). Note that “n”, as described in the background, in an embodiment, may correspond to each STS-1 signal carried per frame. Thus, for example, in an embodiment there is forty eight 2:1 multiplexers for a framer 201 that corresponds to an OC-48 framer (i.e., n=48). The framer logic unit output 209 may be viewed as a bus that collects each 2:1 multiplexer output. The framer logic unit 200 may be viewed as an architectural building block for a networking system. In such an application, the framer logic unit output 209 may be directed to every other framer logic unit in the system. That is, the architecture of the system may be designed to have multiple framer logic units (e.g., one framer logic unit 200 per inbound/outbound line pair coupled to the system).

As such, the framer logic unit 200 is designed to communicate with other framer logic units within the same system. For example, in an embodiment, framer logic unit 200 corresponds to a line interface card (LIC) that plugs into the backplane of a switch. In this case, the framer logic unit output 209 corresponds to a LIC output 209 that may be routed (through a backplane) to every other LIC in the system having the same (or similar) framer logic unit 200 design seen in FIG. 2.

As such, the framer logic unit 200 is also designed to receive each output from the other framer logic units in the system. Thus, for a system having “x”; other framer logic units, framer logic unit 200 receives “x” inputs 212 ₁, 212 ₂, 212 ₃, . . . , 212 _(x). Thus, each input 212 ₁, 212 ₂, 212 ₃, . . . , 212 _(x) corresponds to the output bus (similar to output 209) of another framer logic unit in the system.

Combining each input 212 ₁, 212 ₂, 212 ₃, . . . , 212 _(x) together corresponds to a total input of “xn” signals. That is, in this particular embodiment, as each input has n signals and as there are x inputs, the total number of signals presented to the framer logic unit 200 corresponds to “xn”. The “xn” group of input signals are directed to a pair of (xn):n multiplexers 210, 211. Each (xn):n multiplexer 210, 211 selects “n” of the “xn” input signals.

Each of the 2:1 multiplexers 208 ₁, 208 ₂, 208 ₁, . . . , 208 _(n) receives one of the n outputs from the first (xn):n mutliplexer 210. As described in more detail below with respect to FIGS. 3 and 4, the architectural arrangement of the first (xn):n multiplexer 210 feeding each of the 2:1 multiplexers 208 ₁, 208 ₂, 208 ₃, . . . , 208 _(n) helps provide for efficient link redundancy.

The output of the second (xn):n multiplexer 211 corresponds to outbound signals 205 that are transported over the outbound networking line 203. Note that the second multiplexer 211 may be used to establish the switching fabric of the networking system. That is, as the output signals of every framer logic unit may be presented to the second multiplexer 211, any input signal can be directed to the input of framer 201. As every framer logic unit may receive the output of the other framer logic units within the system, an entire switching fabric for a networking system may be established by configuring the selection of particular output signals from each (xn):n multiplexer that feeds input signals to a framer.

FIG. 3 shows a 1+1 Fiber Facility Protection (FFP) or Unidirectional Path Switched Ring (UPSR) redundancy scheme that employs the exemplary framer logic unit of FIG. 2. Under a 1+1 FFP redundancy scheme or a UPSR redundancy scheme, a “working” pair of networking lines (e.g., networking line pair 302 a, 303 a) are considered the primary networking lines used for communication between the pair of nodes 370, 380 that are coupled by the pair. Should the working pair of networking lines 302 a, 303 a fail, however, a “protection” pair of networking lines 302 b, 303 b are enabled.

A networking system built with framer logic units 200 as discussed above allows for efficient 1+1 FFP or UPSR redundancy because redundancy “hooks” are built into the framer logic unit design. Specifically, note that FIG. 3 shows a first node 370 and a second node 380 that are each constructed with the framer logic units 300 a, 300 b, 300 c, and 300 d as described above with respect to FIG. 2.

Networking system 370 includes framer logic units 300 c and 300 d while networking system 380 includes framer logic units 300 a and 300 b. Note that the framer logic units within the same system are coupled as described above with respect to FIG. 2. That is, the output 309 a of framer logic unit 300 a is shown coupled to an input 312 b ₂ of framer logic unit 300 b. Similarly, the output 309 c of framer logic unit 300 c is shown coupled to an input 312 d ₂ of framer logic unit 300 d.

Note that the output 309 b of framer logic unit 300 b may be coupled to an input of framer logic unit 300 a and the output 309 d of framer logic unit 300 d may be coupled to an input of framer logic unit 300 c; however, for ease of drawing, these couplings are not shown in FIG. 3. Within the first networking system 370, the second (xn):n multiplexers 311 c, 311 d of each framer logic unit 300 c, 300 d are identically configured.

That is, both (xn):n multiplexers 311 c, 311 d present the same collection of signals to each of their respective framers 301 c, 301 d. As such, networking lines 302 a, 302 b are configured to send the same information from system 370 to system 380. Similarly, within the second networking system 380, the second (xn):n multiplexers 311 a, 311 b of each framer logic unit 300 a, 300 b are identically configured such that the same information is sent from system 380 to system 370 over networking lines 303 a and 303 b.

The output of framer logic units 300 a and 300 c correspond to the inbound signals 304 a, 304 c from framers 301 a and 301 c, respectively. That is, the 2:1 multiplexers 308 a ₁ through 308 a _(n) of framer logic unit 300 a are configured to select the framer 301 a inbound signals 304 a rather than the output signals from the first multiplexer 310 a. Similarly, the 2:1 multiplexers 308 c ₁ through 308 c _(n) of framer logic unit 300 c are configured to select the framer 301 c inbound signals 304 c rather than the output signals from the first multiplexer 310 c.

The first (xn):n multiplexer 310 b within framer logic unit 300 b is configured to select the output signals from framer logic unit 300 a. Also, the first (xn):n multiplexer 310 d within framer logic unit 300 d is configured to select the output signals from framer logic unit 300 c. As such, first multiplexer 310 b effectively presents framer 301 a inbound signals 304 a to the 2:1 multiplexers 350 within framer logic unit 300 b; and first multiplexer 310 d effectively presents framer 301 c inbound signals 304 c to the 2:1 multiplexers 360 within framer logic unit 300 d.

The 2:1 multiplexers 350, 360 of frame logic units 300 b, 300 d also receive the inbound signals 304 b, 304 d from their respective framers 301 b, 301 d. As such, the 2:1 multiplexers 350 receive the inbound signals 304 b from framer 301 b at one channel input as well as receive the inbound signals 304 a from framer 301 a at the other channel input. Similarly, the 2:1 multiplexers 360 receive the inbound signals 304 d from framer 301 d at one channel input as well as receive the inbound signals 304 c from framer 301 c at the other channel input.

Because networking lines 302 a and 302 b send the same information as discussed above, the 2:1 multiplexers 350 within framer logic unit 300 b effectively receives the same information at both channel inputs. Similarly, because networking lines 303 a and 303 b send the same information as discussed above, the 2:1 multiplexers 360 within framer logic unit 300 d effectively receive the same information at both channel inputs.

As such, the 2:1 multiplexers 350, 360 may easily toggle from the working networking line pair 302 a, 303 a to the protection networking line pair 302 b, 303 b if the working networking line pair 302 a, 303 a should fail. Specifically, during normal “working” mode, the 2:1 multiplexers 350, 360 are respectively configured to enable the inbound signals 304 a, 304 c received from framers 301 a, 301 c. If a failure is detected on networking line pair 302 a, 303 a the selection performed by the 2:1 multiplexers 350, 360 is toggled to produce the inbound signals 304 b, 304 d from the framers 301 b, 301 d at output 309 b and 309 d (rather the inbound signals 304 a, 304 c from framers 301 a, 301 c).

Thus, regardless as to which network line pair is actually used, the output 309 b, 309 d from framer logic units 300 b, 300 d are “looked to” by the networking system 380, 370 to as the source of information from the other networking system 370, 380. As such, either networking system 370, 380 does not experience significant disruption.

FIG. 4 shows an example of 1:N redundancy or 1:1 Bidirectional Line Switched Ring (BLSR) redundancy implemented with the framer logic unit 200 shown in FIG. 2. In either approach, a spare networking line pair 402 _(spare), 403 _(spare) replaces any networking line pair that fails within a group of networking line pairs 402 ₁ through 402 _(N), 403 ₁ through 403 _(N). Note that the framer logic units 400 a ₁ through 400 a _(N), 400 a _(spare) and framer logic units 400 b ₁, through 400 b _(N), 400 b _(spare) each correspond to the framer logic unit design 200 of FIG. 2.

In the approach of FIG. 4, when a particular line pair within the protected group (402 ₁ through 402 _(N), 403 ₁ through 403 _(N)) fails, the second (xn):n multiplexer 411 a, 411 b within each spare framer logic unit 400 a, 400 b are configured to select the outbound signals 305 a, 305 b that were sent over the failed networking line pair. Thus, for example, if networking line pair 402 ₁, 403 ₁ fails, the signals selected for transmission over networking line 403 ₁ are presented to framer 401 a _(spare) for transmission over networking line 403 _(spare). Similarly, the signals selected for transmission over networking line 402 ₁ are presented to framer 401 b _(spare) for transmission over networking line 402 _(spare). The 2:1 multiplexers of the spare framer logic units 400 a _(spare), 400 b _(spare) are configured to select the outbound signals from their respective framers 401 a _(spare), 401 b _(spare).

FIG. 5 shows another framer logic unit embodiment 500 that may be viewed as the framer logic unit 200 of FIG. 2 further including a switching or routing extension 501. The inputs 212 ₁, 212 ₂, 212 ₃, . . . , 212 _(x) to the framer logic unit 500 are coupled to a third (xn):n multiplexer 503 that may select any inbound signal for switching or routing. Routing or switching engine 501 provides packet based (e.g., Internet Protocol (IP) based) switching (e.g., label switching) or routing. The routing or switching engine 501 may be a logic circuit; or a processor that executes software consistent with the routing or switching protocol(s) to be employed; or a combination of logic and processor.

The routing or switching engine 501 assembles packets from the signals 505 ₁, 505 ₂, 505 ₃, . . . , 505 _(n) selected by a third (xn):n multiplexer 503. Based on the destination of a packet (e.g., as indicated in the packet's header), the routing or switching engine 501 determines an appropriate outbound signal 506 ₁, 506 ₂, 506 ₃, . . . , 506 _(n) that the packet should be forwarded to. The packet is then disassembled and sent over the appropriate outbound signal. Note that a second framer logic unit output 502 may be viewed as a bus having each of the switching or routing engine output signals 506 ₁, 506 ₂, 506 ₃, . . . , 506 _(n).

In an embodiment, framer output logic output 502 is sent to every other framer logic unit in the networking system. As such the networking system can be configured to provide packet based routing or switching between any of the n inbound signals 505 ₁, 505 ₂, 505 ₃, . . . , 505 _(n) selected by the third (xn):n multiplexer 503 and any of the “n” outbound signals 506 ₁, 506 ₂, 506 ₃, . . . , 506 _(n) within the networking system.

Note also that embodiments of the present description may be implemented not only within a semiconductor chip but also within machine readable media. For example, the designs discussed above may be stored upon and/or embedded within machine readable media associated with a design tool used for designing semiconductor devices. Examples include a netlist formatted in the VHSIC Hardware Description Language (VHDL) language, Verilog language or SPICE language. Some netlist examples include: a behaviorial level netlist, a register transfer level (RTL) netlist, a gate level netlist and a transistor level netlist. Machine readable media also include media having layout information such as a GDS-II file. Furthermore, netlist files or other machine readable media for semiconductor chip design may be used in a simulation environment to perform the methods of the teachings described above.

Thus, it is also to be understood that embodiments of this invention may be used as or to support a software program executed upon some form of processing core (such as the CPU of a computer) or otherwise implemented or realized upon or within a machine readable medium. A machine readable medium includes any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine readable medium includes read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.); etc.

In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

For example, even though the above description has described a networking system where every framer logic unit 200 couples “n” signals to a framer 201 and every first 210, second 211, and third 503 multiplexers correspond to a (xn):n multiplexer, other embodiments may be realized that deviate from this architecture.

For example, framer logic units within the same networking system may couple different amounts of signals to their respective framer (e.g., some framer logic units may couple “n” signals to their respective framer while other framer logic units may couple more than (or less than) “n” signals to their respective framer. For example, a framer logic unit coupled to a pair of higher speed networking lines may present more signals to its respective framer than a framer logic unit coupled to a pair of lower speed networking lines.

Furthermore a framer logic unit does not necessarily need to receive (at first 210, second 211, and third 503 multiplexers) every inbound signal in the system. As such, in light of the comments above, first 210, second 211, and third 503 multiplexers may exhibit a varied selection ratio from framer logic unit to framer logic unit. That is, some selection ratios within a networking system may be configured at (xn):n. However, selection ratios other than (xn):n may exist within the same system. As such, the routing or switching engine 501 may switch or route packets from/to more than n signals or from/to less than n signals. 

1. An apparatus, comprising: a) a first framer; b) a 2:1 multiplexer to receive an inbound signal from the first framer, the 2:1 multiplexer having a first input coupled to the first framer; c) a first mutliplexer to receive at least one signal from a second framer, the 2:1 multiplexer having an input coupled to an output from the first multiplexer; and d) a second multiplexer to receive at least one signal from the second framer, the second multiplexer having an output coupled to an input of the first framer for an outbound signal.
 2. The apparatus of claim 1 wherein the first framer is a SONET framer.
 3. The apparatus of claim 2 wherein the signal corresponds to an STS-1 signal.
 4. The apparatus of claim 1 wherein the first framer has n inbound signals and n outbound signals.
 5. The apparatus of claim 4 wherein n is equal to
 3. 6. The apparatus of claim 4 wherein n is equal to
 12. 7. The apparatus of claim 4 wherein n is equal to
 48. 8. The apparatus of claim 4 wherein n is equal to
 192. 9. The apparatus of claim 1 wherein the first framer is an SDH framer.
 10. The apparatus of claim 9 wherein the signal is an STS-1 signal.
 11. A networking system having a first framer logic unit and a second-framer logic unit, the framer logic unit further comprising: a) a framer; b) a 2:1 multiplexer to receive an inbound signal from the framer, the 2:1 multiplexer having a first input coupled to the first framer; c) a first mutliplexer to receive at least one signal from the second framer logic unit, the 2:1 multiplexer having an input coupled to an output from the first multiplexer; and d) a second multiplexer to receive at least one signal from the second framer logic unit, the second multiplexer having an output coupled to an input of the framer for an outbound signal.
 12. The apparatus of claim 11 wherein the framer is a SONET framer.
 13. The apparatus of claim 12 wherein the signal corresponds to an STS-1 signal.
 14. The apparatus of claim 11 wherein the framer has n inbound signals and n outbound signals.
 15. The apparatus of claim 14 wherein n is equal to
 3. 16. The apparatus of claim 14 wherein n is equal to
 12. 17. The apparatus of claim 14 wherein n is equal to
 48. 18. The apparatus of claim 14 wherein n is equal to
 192. 19. The apparatus of claim 11 wherein the framer is an SDH framer.
 20. The apparatus of claim 19 wherein the signal is an STS-1 signal.
 21. The apparatus of claim 11 wherein each of the framer logic units corresponds to a line interface card.
 22. The apparatus of claim 21 wherein the first and second framer logic unit are coupled together through a backplane.
 23. An apparatus, comprising: a) a first framer; b) a 2:1 multiplexer that receives an inbound signal from the first framer; c) a first mutliplexer that receives at least one signal from a second framer, the 2:1 multiplexer having an input coupled to an output from the first multiplexer; d) a second multiplexer that receives at least one signal from the second framer, the second multiplexer having an output coupled to an input of the first framer for an outbound signal; and e) a third multiplexer that receives at least one signal from the second framer, the third multiplexer having an output coupled to a routing or switching engine that forwards packets received from the third multiplexer output onto another signal.
 24. The apparatus of claim 23 wherein the first framer is a SONET framer.
 25. The apparatus of claim 24 wherein the signal corresponds to an STS-1 signal.
 26. The apparatus of claim 23 wherein the first framer has n inbound signals and n outbound signals.
 27. The apparatus of claim 26 wherein n is equal to
 3. 28. The apparatus of claim 26 wherein n is equal to
 12. 29. The apparatus of claim 26 wherein n is equal to
 48. 30. The apparatus of claim 26 wherein n is equal to
 192. 31. The apparatus of claim 23 wherein the first framer is an SDH framer.
 32. The apparatus of claim 31 wherein the signal is an STS-1 signal. 